According to texts ascribed to Flamel almost 200 years after his death, he had learned alchemical secrets from a Jewish converso on the road to Santiago de Compostela.

[7] There is an old inscription on the wall, which states, "We, plowmen and women living at the porch of this house, built in 1407, are requested to say every day an 'Our Father' and an 'Ave Maria' praying God that His grace forgive poor and dead sinners."

The essence of his reputation are claims that he succeeded at the two goals of alchemy: that he made the philosopher's stone, which turns base metals into gold, and that he and his wife, Perenelle, achieved immortality through the "Elixir of Life".

[9] It is a collection of designs purportedly commissioned by Flamel for a tympanum at the Cimetière des Innocents in Paris, long disappeared at the time the work was published.

With this knowledge, over the next few years, Flamel and his wife allegedly decoded enough of the book to successfully replicate its recipe for the philosopher's stone, producing first silver in 1382 and then gold.

He claimed that the source of the Flamel legend was P. Arnauld de la Chevalerie, publisher of Exposition of the Hieroglyphical Figures, who wrote the book under the pseudonym Eiranaeus Orandus.

Flamel had achieved legendary status within the circles of alchemy by the mid 17th century, with references in Isaac Newton's journals to "the Caduceus, the Dragons of Flammel".

Flamel's reputation as an alchemist was further bolstered in the late 20th century by his depiction as the creator of the titular alchemical substance in the best-selling novel Harry Potter and the Philosopher's Stone[14] and its film adaptation.